This invention relates generally to air intakes for engines, and in particular to a system for mounting and sealing a barrier filter which protects an aircraft engine.
An engine for aircraft propulsion requires intake air that is free from contaminants to provide for efficient combustion and avoid internal damage. The compressor and turbine are designed with small tolerances between moving parts which maximize efficiency, but which also increase vulnerability to damage from small foreign particles. Contamination of intake air, even in a small amount, causes premature wear on engine components, increases maintenance costs, and degrades operational reliability. Unfortunately, aircraft are exposed to contaminants when operating at low altitudes where air is frequently contaminated with material from the ground, such as sand and dust. That problem is aggravated for helicopters due to rotor downwash and prolonged low-altitude operation.
Systems which remove foreign particles from intake flow have been developed to protect the engine from damage. In many instances, such a system includes an intake housing having a contaminant separator, such as a filter, positioned in advance of the engine inlet, with airtight seals at interfaces to prevent entry of unfiltered air. Effective sealing is difficult to implement and maintain because the engine moves relative to adjacent parts of the airframe as its power setting varies. For example, the front end of the engine may deflect about one inch as its power increases, with the movement being in a direction having all three directional components with respect to the airframe (e.g., forward, inboard, and down). Unfortunately, seals have been stiff or insufficiently flexible to move in this way while maintaining airtight integrity. They have typically been made of stiff materials because they are located where they must withstand pressure in the inlet. Further, seals are prone to fail when exposed to strong differential pressures if the engine should experience a surge instability that suddenly increases inlet pressure. Aggravating the difficulty is that the filter must be accessible for maintenance actions, cannot obstruct accessibility to the engine or airframe, and should not introduce loads to the inlet.